The use of helmets to protect the head from injury has been done through the centuries, and for a variety of activities ranging from warfare to the more common uses today of sports and recreation. Typical helmet construction consists of a rigid or semi-rigid shell formed into a generally domed-shape, which covers the majority of the user's head and frequently incorporates a chinstrap to secure the shell in the preferred position on the head. Depending upon the shell construction, padding or cushioning may also be provided along the inside of the shell for increased comfort, better fit and to assist in the absorption of any impact forces.
Helmets from their first use to today, have essentially been an artificial skull over the human skull and thus only duplicate the same protection the natural skull is already providing, without adding any more safety dimensions. In fact, the extra ‘skull’ serves to increase the weight of the head relative to the neck muscles, which is well-researched cause of both soft tissue and bone injuries. More important for injuries, this additional weight increases the acceleration potential ((increased) mass×velocity) of the brain inside the cranium, after impact.
Conventional helmets are formed from molded semi-rigid polystyrene or Styrofoam™ bonded to a plastic outer skin, or the hard rigid shell is lined with soft padding. There is an important disadvantage and negative safety feature inherent with both of these common conventional helmet styles. In order to provide sufficient protection from impact forces, heretofore it has been the practice of the helmet manufacturers to form the polystyrene shell layer with a thickness of one inch or more, and if the padding is for comfort it is often of similar thickness. As a result, when worn, these sports helmets project outwardly a distance of two inches or more from the wearer's head, increasing the diameter of the natural skull and adding physical disproportion of head to shoulder/torso, for optimal muscular control.
Upon impact from anything other than a true perpendicular force vector, the skull/helmet combination acts as a fulcrum as the neck and body ‘bends’ around it. With increased diameter, the range and magnitude of ‘bend’ at the fulcrum is dramatically increased and ultimately, the quantity and quality of associated injuries. This is one of the most common ways for avulsion of bone, discs and muscles and it is the classical method for cervical nerve root stretch, rupture or avulsion. Termed a ‘zinger’ in its mild, temporary form, permanent total nerve loss results when the ‘bending’ injury is more severe. Larger diameter and/or added weight invariably increase rotational force potential and rotation, according to whiplash research, is the most destructive.